Grinder

ABSTRACT

A grinder is disclosed which has a housing ( 12 ) in which a rotatable disc ( 60 ) is mounted. The disc ( 60 ) is rotated by a motor ( 40 )and the disc ( 60 ) has a periphery which is adjacent an inner stationary wall ( 102 ) of the housing ( 12  ). An air inlet ( 108 ) is arranged below the disc and the disc carries vanes ( 100 ) so that when the disc rotates, an annular air stream is created at the periphery of the disc in which a grinding zone is established between the periphery of the disc and the stationary wall ( 102 ) for grinding material into small particles. The grinding zone includes an annular flow of heavy gas R 1 . A material inlet ( 20 ) is provided for allowing material to enter the housing ( 12 ). Large material is grounded by energy intensification after it hits the disc ( 60 ) and collides with the inner wall ( 40 ) of the housing so as to break down the material into smaller particle size, which can then move to the grinding zone at the periphery of the disc ( 60 ) to be further ground into small particles. The small particles are collected through an outlet ( 16 ) and may be supplied to separators for separating the small particles from exhaust air from the housing ( 12 ).

FIELD OF THE INVENTION

This invention relates to a grinder for reducing material to smallparticles which can then be used, for example, as a fuel, fertiliser, oran additive to other constituents, broken down small size particles forconvenient waste disposal, providing particles for use in industry, andalso for separating material. In many cases, it is necessary for thesmall particles to be reduced down to small particles which have a sizein the range of 5 to 50 microns and in some cases, less than 5 microns.

BACKGROUND ART

Many devices exist that can reduce material to small particle sizes, butmost are large, slow, heavy, and consume large amounts of energy.However, very few machines exist which can economically reduce particlesdown to very small fine particle sizes.

Grinding of materials to very small particles is carried out by avariety of machines. These machines employ two main processes. The firstand most common, is by crushing the material between hard movingelements made from such materials as steel or silicates until theparticles are of the required size. Repeated recycling may be employedto aid the process. Such machines are rolling, ball or hammer mills.

The second method is by employing high-energy impact. Machines usingthis principle cause high speed, hard moving elements, to collide withthe particles to be ground. The particles to be ground are usuallytransported into and out of the impact area by gravity and by a gas,usually air. In some cases, material to be ground is carried only bygravity into the impact zone in the same way. As well as collisions withthe grinding element, there are particle to particle collisions.However, these impacts make only a very small contribution because theparticles are of much the same kinetic level and are moving in much thesame direction. To achieve significant particle size reduction,recycling of the process must also be employed. A beater hammer mill istypical of such machines.

The crushing process is slow and usually limited in the mining andprimary metallurgy industry. Impact grinding has the potential for fastthroughput and great size reduction for other industrial and commercialparticle grinding. The problem with present impact machines is thatparticle to particle impacts make only a small contribution, and hencethe necessary energy level from the momentum transfer from the impactingelements must be at the highest energy necessary to break up theparticles, that is the energy levels of the particles remain only ashigh as the initial impact.

A need therefore exists for a small, even portable machine that canachieve these results fast and economically.

SUMMARY OF THE INVENTION

An object of a first invention is to provide an impact particle grinderwhich can reduce gross particles down to a much smaller particle size.

A first invention may be said to reside in an impact particle grinder,comprising;

-   -   a housing having an inner wall;    -   a grinding disc mounted in the housing for rotation within the        housing;    -   means for rotating the grinding disc;    -   an inlet for depositing material onto a first location on the        rotating disc, so kinetic energy is supplied to the material        from the disc to fling the material against the inner wall of        the housing, and material deflected from the housing falls back        onto the disc at a second location radially outwardly of the        first location so that further kinetic energy is imparted to        that material to provide an energy intensifying process as        material continues to impact against the inner wall of the        housing and fall back on a radially more outward part of the        rotating disc, and wherein particle to particle collisions        within the housing and collisions with the rotating disc and        inner wall break down the material to produce small particles;        and    -   outlet means for discharge of the small particles from the        grinder.

Thus, the impact grinder works using two principles. The first is byrepeatedly injecting energy at higher and higher levels into theparticles as they are reduced in size. This is a continuous energyintensifying process.

The grinder therefore processes material step by step to higher energylevels as it impacts further out towards the periphery of the disc. Thisresults in very great size reduction. Recycling therefore is onlyemployed by the machine to act upon particles, which have not reachedthe requisite energy level by the time they impact with a radially mostoutward part of the disc.

Depending on the size of the particle required, the particles can simplybe discharged from the machine. However, if very fine particles arerequired, the particles can undergo further processing to reduce theparticles to fines.

In the preferred embodiment of the invention, the additional grinding toproduce the small particles is performed in the grinder by establishinga further grinding zone between the periphery of the spinning disc and astationary wall of the grinder. This embodiment requires the inventionto operate in a gas rather than a vacuum, with the gas usually simplybeing air.

While operating in a transport medium such as air, each particle will,as it moves to the periphery and into the grinding zone. The groundingzone is formed by a sheer zone which causes comminution of the particlesto form the small particles.

In the preferred embodiment of the invention, the inner wall of thehousing is of inverted conical shape so that deflection of material fromthe inner wall tends to direct the material to the second location whichis a small distance from the first location, thereby producing asignificant number of impacts of the material with the disc as thematerial bounces between the disc and the inner wall. The result of thisincreased number of collisions produces a greater number of impactswhich impart increased kinetic energy to the material, and thereforegreater breakdown of the material due to those impacts and particle toparticle collisions.

In one embodiment of the invention the grinder includes hot air inletmeans for introducing hot air into the housing adjacent the disc fordrying the material as the material is ground.

In one embodiment the grinder also includes inert gas introduction meansfor introducing inert gas to mix with the ground particles.

In one embodiment of the invention the outlet means is arranged abovethe disc.

In one embodiment, the outlet means comprises a plurality of outletswhich are arranged at different heights above the disc so that particlesof different sizes are collected in each of the outlets, the outletsbeing provided in a housing wall portion which is of conical shape.

The outlet means may include a recirculator for recirculating smallparticles from the outlet means back to the housing for reprocessing inthe housing.

In one embodiment, the outlet means is connected to a cyclone particlecollector.

Preferably the cyclone particle collector comprises means for creating acircular flow of air in the cyclone, inlet means connected to the outletmeans for receiving particles from the housing and for conveying theparticles into the cyclone for circulation in the circular air flow inthe cyclone, an air outlet tube in the cyclone and a particle outlet inthe cyclone, and wherein particles trapped in the circular flow of airare conveyed about the cyclone with the circular flow of air andseparated from air flow so that the particles can be collected in theparticle outlet and air exit the cyclone through the air outlet.

Preferably the air inlet means for creating the circular flow of aircomprises a hot air inlet and a heater for heating air for supply to thehot air inlet.

In one embodiment of the invention, the disc has an outer peripherywhich is in close proximity to the inner wall of the housing so thatwhen the disc is rotated by the rotating means, an annular rotatingstream of air is formed between the periphery of the disc and the innerwall, so a sheer zone is created between the periphery of the disc andthe inner wall so that when particles enter the space between the discand the inner wall, they are subject to the shear zone to further reducethe particles to small particles.

An air inlet means is preferably provided below the disc in the housingfor allowing air to enter the housing from below the disc to cause theair annulus to spill up the inner wall of the housing so that finelyground particles trapped in the rotating stream of air are carried bythe spill of air to the outlet means.

In another embodiment of the invention, the outlet means is arrangedbelow the disc. This embodiment would be used in environments in whichthe grinder is operating in a vacuum or extremely low air pressureenvironments, and in which the air stream at the periphery of the discis therefore not created. Thus, in this embodiment, small particles haveno option but to fall under the influence of gravity in the spacebetween the periphery of the disc and the inner wall of the container tothe outlet means below the disc.

In one embodiment the disc includes a plurality of vanes for impartingmomentum to the air when the disc rotates to create the annular rotatingstream of air between the periphery of the disc and the wall to createthe sheer zone.

Preferably the vanes are angled upwardly relative to the horizontal sothat the rotating stream of air is directed upwardly above the disc tofacilitate the spill of air up the inner wall.

Preferably the inner wall of the housing includes a separate cylindricalwall which includes a contoured wall portion for trapping material sothe material remains in the annular airflow for a long period to breakdown the material to small particles, before the small particles travelin the spill of air up the inner wall to the outlet.

This invention also provides a method of impact grinding a material,comprising;

-   -   supplying the material to a grinder which has a housing having        an inner wall and a rotating disc mounted in the housing;    -   wherein the material supplied is deposited onto a first location        on the rotating disc, so kinetic energy is supplied to the        material from the disc to fling the material against the inner        wall of the housing, and material deflected from the housing        falls back onto the disc at a second location radially outwardly        of the first location so that further kinetic energy is imparted        to that material to provide an energy intensifying process as        material continues to impact against the inner wall of the        housing and fall back on a radially more outward part of the        rotating disc, and wherein particle to particle collisions        within the housing and collisions with the rotating disc and        inner wall break down the material to produce small particles;        and    -   collecting the small particles from the grinder.

A second invention is concerned with the breakdown of material intosmaller particles.

This invention provides a grinder for producing small particles frommaterial, comprising:

-   -   a housing having a substantially inner wall;    -   a disc mounted in the housing and having a periphery adjacent        the inner wall;    -   a motor for driving the disc so the disc rotates about a        substantially vertical axis;    -   a plurality of vanes on the disc for creating an annular flow of        gas between the periphery of the disc and the inner wall to        create a sheer zone between the inner wall and the periphery of        the disc;    -   an inlet in the housing for receiving the particulate material,        so the particulate material is able to migrate to the sheer zone        between the periphery of the disc and the inner wall and be        broken down to small particles; and    -   a small particle outlet for allowing outlet of the small        particles from the housing.

In this invention the particulate material may be delivered to thehousing from an inlet direct to a location near the periphery of thedisc for substantially direct feeding into the sheer zone.

Thus, in this embodiment the inlet may comprise an inlet tube extendingwithin the housing from an upper portion of the housing to a positionadjacent the periphery of the disc.

However, in another embodiment, the particulate material may be grossmaterial which is first broken down by impact with the disc and thehousing into small particle size which small particles then move to thesheer zone for further breakdown into small particles. In this latterembodiment the inlet generally comprises a tube which delivers the grossparticulate material to a location inwardly of the periphery of thedisc.

Preferably the housing has a gas inlet below the disc and the vanes arelocated on a lower surface of the disc for collecting the gas anddirecting the gas to the periphery of the disc to provide energyintensification to the gas so that the gas at the periphery of the discmoves with high speed, and the gas adjacent the stationary inner wall isat relatively low speed.

Preferably the grinding zone comprises a first region between the wallof the housing and an intermediate location between the wall and theperiphery of the disc for establishing a heavy gas, and a second regionbetween the periphery of the disc and the intermediate location forreceiving particles from the disc so those particles can move into theheavy gas and be ground into small particles.

Preferably a sheer zone is created at the intermediate location betweenthe first and second regions.

Preferably the vanes are located on the lower surface of the disc andare directed upwardly so that the vanes direct the gas to the peripheryof the disc and upwardly relative to the disc so that the annular flowof gas created by each of the vanes between the disc and the inner wall,and within the confines of the disc for a short time period and thenmoves upwardly relative to the disc in annular fashion adjacent theinner wall of the housing.

Preferably the housing has an exhaust gas outlet arranged substantiallycentrally of the disc.

Preferably a standing wave is created between the exhaust gas outlet andthe periphery of the disc so that particles which are broken down intosmall particles in the sheer zone are able to move upwardly with theairflow adjacent the inner wall of the housing to the outlet, or moveinwardly of the disc where they meet the standing wave and are directeddown back to the upper surface of the disc and move along the uppersurface of the disc back to the sheer zone for further grinding, ortravel with the exhaust gas to the exhaust outlet.

Preferably the outlet is connected to a first cyclone for separating gasfrom the small particles so the small particles can be collected at anoutlet of the first cyclone.

Preferably the exhaust gas outlet is connected to a second cyclone sothe gas and small particles can be separated in the second cyclone toenable the small particles to be collected at an outlet of the secondcyclone.

Preferably the first cyclone has a gas exhaust outlet which is connectedto the second cyclone so that any small particles which remain in thegas exhausted from the first cyclone are fed to the second cyclone forseparation from the gas in the second cyclone.

Preferably the outlet from the first cyclone includes a gas lock forpreventing high pressure gas from exiting the outlet and blowing smallparticles into the atmosphere.

Preferably the outlet from the second cyclone also includes a gas lockfor preventing high pressure gas from exiting the second cyclone throughthe outlet.

This invention also provides a method of producing small particles frommaterial, comprising:

-   -   supplying the material to a housing having a substantially inner        wall and a rotating disc mounted in the housing and having a        periphery adjacent the inner wall so that the disc creates an        annular flow of gas between the periphery of the disc and the        inner wall to create a sheer zone between the inner wall and the        periphery of the disc;    -   allowing the material to migrate to the sheer zone between the        periphery of the disc and the inner wall and be broken down to        small particles; and    -   collecting the small particles from the housing.

Preferably the method includes allowing the gas to enter the housingfrom below the disc and providing vanes on a lower surface of the discfor collecting the gas and directing the gas to the periphery of thedisc to provide energy intensification to the gas so that the gas at theperiphery of the disc moves with high speed, and the gas adjacent thestationary inner wall is at relatively low speed, and wherein thegrinding zone is created by the establishment of:

-   -   (a) a heavy gas formed from a mixture of the gas and minute        particles in a first region between the inner wall and an        intermediate position between the disc and the inner wall;    -   (b) a second region for receiving larger particles to be ground        into the smaller particles, between the intermediate position        and the periphery of the disc;    -   (c) a sheer zone between the first and second regions; and        wherein particles in the first region pass through the sheer        zone, and some are comminuted into heavy gas particles and        others which are not sufficiently small to behave as gas        particles are either ejected back to the first region for        further grinding as those particles re-enter the heavy gas        through the sheer zone, or move out of the grinding zone for        collection from the housing.

Preferably the annular flow of gas created by each of the vanes betweenthe disc and the inner wall is maintained within the confines of thedisc and at the sheer zone for a short time period and then movesupwardly relative to the disc in annular fashion adjacent the inner wallof the housing.

Preferably the method comprises extracting gas from an exhaust outletarranged substantially centrally of the disc.

Preferably the method further comprises creating a standing wave betweenthe exhaust outlet and the periphery of the disc so that particles whichare broken down into small particles in the sheer zone move upwardlywith the airflow adjacent the inner wall of the housing to the outlet,or move inwardly of the disc where they meet the standing wave and aredirected down back to the upper surface of the disc, and move along theupper surface of the disc back to the sheer zone for further grinding,or travel with the exhaust gas to the exhaust outlet.

Preferably the method further comprises supplying the collected smallparticles to a first cyclone for separating gas from the small particlesso the small particles can be collected at an outlet of the firstcyclone.

Preferably small particles collected at the exhaust outlet are suppliedto a second cyclone so the gas and small particles can be separated inthe second cyclone to enable the small particles to be collected at anoutlet of the second cyclone.

The invention also provides a grinder for producing small particles frommaterial, comprising:

-   -   a housing having an inner wall;    -   a rotatable mechanical member in the housing having a periphery        adjacent the inner wall;    -   a drive for driving the rotatable member for causing the        rotatable member to create an annular flow of air between the        periphery of the member and the inner wall, and for establishing        a grinding zone between the inner periphery and the wall which        comprises:    -   (a) a first region in which a heavy gas is established, the        first region being between the inner wall and an intermediate        position between the periphery of the member and the inner wall;    -   (b) a second region for receiving relatively large particles        compared to the particles which make up the heavy gas, the        second region being between the intermediate position and the        periphery of the mechanical member; and    -   (c) a sheer zone between the first and second regions at the        intermediate location; and        wherein the relatively large particles received in the first        region come into contact with the heavy gas particles across the        sheer zone where the relatively heavy particles are comminuted        into smaller particles, some of which add to the heavy gas        within the first region and the other of which form small        particles of a size which do not behave as a heavy gas, and        wherein the small particles, together with some of the particles        which make up the heavy gas and other larger particles from the        first region move out of the grinding zone with an annular flow        of air from the grinding zone and travel to a first collection        outlet for collection or fall back to the mechanical member and        again travel to the first region for further grinding in the        grinding zone.

The invention still further provides a method of grinding material,comprising:

-   -   creating a grinding zone having a first annular region in which        an annular flow of heavy gas is established and a second region        spaced from the first region by a shear zone;    -   directing the material into the grinding zone so the material        passes from the second region to the first region across the        shear zone into the annular flow of heavy gas and is comminuted        into smaller particles by contact between heavy gas particles in        the heavy gas and the material; and    -   collecting the comminuted particles.

A third invention relates to a grinding installation for grindingmaterial into small particles.

This invention provides a grinding installation for producing smallparticles from material, comprising a grinder having:

-   -   (a) a housing having a stationary inner wall;    -   (b) a disc mounted in the housing and having a periphery        adjacent the inner wall;    -   (c) a motor for driving the disc so the disc rotates about a        substantially vertical axis, and whereby small particles are        produced by breakdown of material impacting with the disc and        the inner wall and/or in a grinding zone between the periphery        of the disc and the inner wall;    -   (d) an air inlet in the housing;    -   (e) an air exhaust outlet from the housing; and    -   (f) a particle outlet from the housing;    -   a first separator connected to the particle outlet for        separating air from the small particles and for delivering the        small particles to a small particles outlet; and    -   a second separator connected to the exhaust air outlet for        separating small particles in the exhaust air from the exhaust        air and delivering the small particles to a second small        particles outlet.

Preferably the first separator has a first exhaust air outlet and thefirst exhaust air outlet is connected to the second separator.

Preferably the first separator comprises a cyclone separator.

Preferably the second separator comprises a second cyclone separator.

A fourth invention provides a grinder for producing small particlescomprising:

-   -   a first region for establishing a heavy gas, a second region        spaced from the first region and a shear one between the first        and second regions when the grinder is in use;    -   a material inlet for delivery material so the material passes to        the first region for grinding; and    -   an outlet for collecting the small particles.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred embodiments of the invention will be described, by way ofexample, with reference to the accompanying drawings in which:

FIG. 1 is a view of a particle grinder according to one embodiment ofthe invention;

FIG. 2 is a cross-sectional view through the grinder housing of FIG. 1;

FIG. 3 is a detailed view of part of the grinder housing of FIG. 2;

FIG. 4 is a perspective view of a particle grinder according to anotherembodiment; and

FIG. 5 is a cross-sectional view through the embodiment of FIG. 4.

FIG. 6 is a schematic view showing particle breakdown and illustratesenergy intensification during particle breakdown;

FIG. 7 is a cross-sectional view through a cyclone collector shown inFIG. 1; and

FIG. 8 is a view of a second embodiment of the invention;

FIG. 9 is a detailed cross-sectional view of a grinding housingaccording to the embodiment of FIG. 8;

FIG. 9A is an underneath view of a disc used in the preferredembodiments showing the configuration of vanes on the disc;

FIG. 10 is a cross-sectional view through a first cyclone used in theembodiment of FIG. 8;

FIG. 11 is a view of a second cyclone used in the embodiment of FIG. 8;

FIGS. 12 and 13 show a gas lock used in the embodiment of FIG. 8;

FIG. 14 is a schematic diagram showing pressure variation used toexplain the manner in which the embodiments of FIGS. 1 to 7 and 8 to 13operate;

FIG. 15 is a diagram similar to FIG. 14 but showing speed differential;

FIG. 16 is a schematic diagram illustrating the primary grinding zone ofthe preferred embodiments;

FIG. 17 is a side view partly cut away to show operation of thepreferred embodiment of the invention;

FIG. 18 is a schematic diagram showing air stream tubes which arecreated during operation of the preferred embodiments of the invention;

FIG. 19 is a graph showing experimental actual measured particle sizedistribution;

FIG. 20 is a graph showing full particle distribution;

FIG. 21 is a graph showing particle sizes of small particles collectedfrom a small particles outlet from the grinder of the preferredembodiment; and

FIG. 22 is a graph showing particle sizes of small particles collectedin a second separator in the preferred embodiment of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

With reference to FIG. 1, a grinder installation 10 is shown which has agrinder 11 having grinder housing 12, and a cyclone particle separator14. The housing 12 communicates with the cyclone 14 by a small particlesoutlet tube 16 from the housing 12 and an air exhaust tube 18 extendingfrom the housing 12 to the cyclone 14. An inlet tube 20 for supply ofmaterial also communicates with the housing 12.

The cyclone 14 has a small particles outlet tube 22 and an air exhaustoutlet tube 24. An air heater 26 is provided for heating air and forsupplying hot air through delivery tube 28 to valve 30. A first inlet 32is coupled between the valve 30 and the housing 12 for selectivelysupplying hot air to the housing 12, and a second inlet tube 34 extendsbetween the valve 30 and the cyclone 14 for providing hot air into thecyclone 14 for creating a circular cyclonic flow of air within thecyclone 14.

The housing 12 is supported on a cylindrical casing 36 and flange 38which connects to an electric motor 39.

As is best shown in FIG. 2, the housing 12 is formed from a conicalupper casing 40 which tapers inwardly from flange 42 at the bottom ofthe casing 40 to upper flange 44 at the top of the casing 40. The flange42 is connected to a lower dish casing 46 via flange 48. The casing 40is connected to a cap casing 50 by flange 44 on the casing 40 and flange52 on the casing 50. The particle outlet conduit 16 communicates withthe cap casing 50.

A disc 60 is mounted in the casing 46 and is supported on a shaft 62which is arranged in bearings 66 and bushes 68 within the cylindricalcasing 36. Thrust bearings 70 may also be provided if desired.

The cylindrical casing 36 is secured to the base 47 of the dish casing46 by flange 68 a on the cylindrical casing 38.

The flanges 44 and 52, the flanges 42 and 48 and the flange 70 and base47 can be connected together by bolts 71, which are shown joining theflanges 44 and 52, as well as the flanges 42 and 48.

If the grinder is to be used for the breakdown of soft or very lightmaterial, such as feathers or the like, a separate removable cylinder 74may be located in the housing 12 as shown in FIGS. 1-3. The cylinder 74has a recessed contoured wall portion 102 which forms a step 103 withinner wall portion 103 a. The purpose of this configuration will bedescribed in more detail hereinafter.

The material inlet tube 20 is also used in situations where very soft orlight material is to be ground. This tube 20 is also used if liquid orsludge type material is to be broken down by the grinder. In the case oflight or soft material, the material can be directed through the tube 20with an airflow injected into the tube 20 for carrying that materialalong the tube 20 to outlet end 80. As is shown in FIG. 2, the outletend 80 terminates at a distance radially outward from the centre of thedisc 50. The location of the end 80 is selected so that at that positionof the disc, the kinetic energy which will be imparted to the materialexiting the end 80 is such that the material will be bounced off thedisc and will not merely stick to or sit on the disc. In the case ofsludge or other liquid material, if the sludge or liquid material isdeposited on a central portion of the disc, it is possible that thespeed of rotation at that point will not be sufficient enough to impartsufficient kinetic energy to the disc to cause the material to be flungfrom the disc towards the wall 40. The material may well just stick tothe disc or sit on the disc, and therefore not undergo breakdown. Bydirecting the material to a radially outer part of the disc, thematerial will initially have sufficient kinetic energy imparted to it bythe rotating disc to cause the material to bounce from the disc towardsthe wall 40 so that the collisions will occur which will break down thematerial.

As is best shown in FIG. 3, the disc 60 comprises an upper plate 85which is supported on flange 86 of the shaft 62. A lower plate 88 isarranged below the plate 85 and connected to the plate 85 by bolts orother suitable fasteners 90. The plate 85 has a bevelled lower surface90 and the plate 88 has an outer peripheral part 92 which is angled withrespect to the remainder of the plate 88 so as to be substantiallyparallel to the lower bevelled surface 90. A plurality of vanes 100 areprovided between the surface 90 and the inclined part 92 of the lowerplate 88.

The inner wall 74 has a contoured wall portion 102 adjacent theperiphery of the disc 60.

When the disc 60 is rotated, the disc 60 creates an annular or acircular air flow adjacent the periphery of the disc 60 between the disc60 and the wall 74. By angling the vanes 100 upwardly, as is shown inFIG. 3, the circular air flow is directed upwardly along inner wall ofthe casing 40 (or cylinder 74 if in place) to facilitate spill of theannular air flow up along the inner wall 40 towards the outlet, which inthe embodiment of FIGS. 1 and 2 is formed by the pipe 16 in cap casing50.

The base 47 of the casing part 46 has a plurality of air inlet openings108 which also facilitate spillage of air up along the inner wall 40.Air can enter the inlets 108 and is drawn by the low pressureenvironment at the periphery of the disc (as will be described in moredetail hereinafter) so as to tend to push the annular air stream at theperiphery of the disc upwardly along the wall 40.

FIGS. 5 and 6 show a second embodiment of the invention in which likereference numerals indicate like paths to those previously described.Thus, the disc 60, casing 40, casing 46 and shaft 62 are exactly thesame as previously described. The disc 60 also creates the annular airflow in the same manner as previously described. In this embodiment, thecap 50 is replaced by an upper conical casing 120 which carries amaterial inlet 122, which is arranged substantially centrally withrespect to the disc 60. This embodiment is intended to be used to breakdown relatively large or heavy material (gross material) which isunlikely to stick or sit on the rotating disc 60 and therefore can be,and most desirable is, deposited generally centrally on the disc 60rather than some distance radially outwardly of the disc 60 as in thecase of the embodiment of FIGS. 1-3.

The casing 120 has a plurality of outlet openings 124 and 126 which areformed in the conical wall of the casing 120. The outlet openingsprovide for separation of particles of different sizes carried by theair flow which spills up the inner surface of the casing 40 and then upthe inner surface of the casing 120. This separation process will bedescribed in more detail hereinafter.

Also, in the embodiment of FIG. 5, the grinder may be used to separateconglomerate material such that stones or pebbles of a particular sizewhich are fed into the grinder through the inlet 122 initially deflectoff the disc 60 and are collected at outlet 130. Material of a differentsize remains in the grinder and is broken down in the manner which willbe described hereinafter. In this embodiment, a shelf 132 could beprovided below the opening 130 to facilitate removal of the materialfrom the opening 130. This simply enables conglomerate material to beloaded into the grinder and for a particular particle size to beinitially collected without any substantial breakdown because thatparticle size will initially deflect from the mid portion of the disc tothe region of the opening 130 for collection. Smaller and largerparticles will tend to travel upon different trajectories towards thewall 40 and therefore collide with the wall 40 for breakdown intosmaller particle size, as will be described hereinafter.

FIG. 6 shows breakdown of gross material, such as that in a size rangeof 100 mm to 300 mm. The gross material is deposited into the grinderfrom above the disc 60 through inlet 122 (FIG. 6). A lump of materialdropped into the inlet 122 will fall (arrow A) on the disc at a firstlocation near the centre of the disc and will absorb momentum and bethrown by centrifugal force (arrow B) against the internal surface 41 ofthe inverted conical casing 40. The material will begin initialbreakdown on first impact with the disc 60 and then on impact with theinternal surface 41. The material will then fall, depending on its size,back towards the disc 60 (arrow C), and contact the disc 60 at a second.position on the disc 60 radially outwardly of the first position. Thatimpact will again cause breakdown and throw the material towards theinner surface 41 (arrow D) where further breakdown will occur and thematerial will again fall (arrow E) towards the disc 60 for a stillfurther impact, still further radially outwardly, of the disc 60. Thisprocess continues as the material is bounced back and forward betweenthe disc 60 and the internal surface 41 as shown by arrow F, G, H, I, Jand K. These impacts will therefore break up the material into smallerparticle size. The shape of the casing 40 which is an inverted cone willdeflect the material impinging on the inner surface 41 back towards thedisc 60 so that it impinges on the disc 60 radially outwardly from theprevious impact position a distance not too far radially outwardly fromthe initial impact. Thus, several impacts with the disc 60 and the innerwall 41 will occur as the material breaks down and gradually movestowards the outer periphery of the disc 60. As is apparent from FIG. 6,the initial impact of the material falling in the direction of arrow Ais close to the centre of the disc and therefore impacts on a part ofthe disc which is rotating at slower speed than points of the discradially outwardly towards the periphery of the disc. That is, whilstall points of the disc on a radial line are travelling with the sameangular velocity, the actual speed of each point increases radiallyoutwardly because of the increased distance traversed by that pointduring each revolution of that disc. Since the initial impact belowarrow A is inwardly of the disc, the amount of energy imparted to thematerial is relatively small. As the material bounces back and forwardbetween the disc and the wall 40, and falls on radially more outwardparts of the disc 60, the speed of the disc is greater at thosepositions of impact, thereby imparting increased kinetic energy to thematerial. Thus, the bouncing back and forward of the material betweenthe disc 60 and the wall 40 intensifies the kinetic energy of thematerial, thereby increasing the energy of the material for particle toparticle collisions and also collisions with the wall 40 and the disc60. These collisions break down the material into ever smaller sizes,with the smaller size particles gradually finding their way towards theperiphery of the disc 60.

It should also be noted in FIG. 6 that the direction a piece of materialtravels after deflection from the wall 40 and the direction a piece ofmaterial travels towards the wall 40 are almost linear, or in otherwords head-on, thereby causing maximum impact in particle to particlecollisions as the material bounces back and forward between the disc 60and wall 40.

It should of course be understood that the movement of the materialbetween the disc 60 and the wall 40 is somewhat chaotic because of thebreakdown of the material and therefore the change in size of thematerial, as well as the angle of collisions, which will deflect thematerial in various different directions. However, the general travel ofmaterial as the material breaks down will be in accordance with thearrows shown in FIG. 6, whereby relatively large material commencesimpact at a radially inner location of the disc with gradually smallerparticles during the breakdown process finding their way towards theedge of the disc, and in general, a significant number of collisionsbetween the disc 60 and the wall 40 may well take place before thematerial has broken down to a small size where it forms relatively smallparticles towards the periphery of the disc 60.

Whilst it is preferred that the wall 40 have an inverted conical shape,as is shown in FIGS. 1-6, a wall shape of other configurations, such asgenerally cylindrical, are also possible. However, a cylindrical has adisadvantage that material deflected from the wall is likely toinitially land a greater distance towards the periphery of the disc asit rebounds from the wall, thereby decreasing the number of impactswhich occur between the rotating disc and the wall 40. The reason forthis is that the point of impact on the cylindrical wall will always beoutwardly of the disc, and therefore the trajectory of the material backonto the disc is likely to take the material to a radially more outerlocation on the disc. Because the conical wall effectively extendsinwardly and over the disc 60, impacts of material travelling in thedirection of arrow B occur above a midpoint of the distance between thecentre of the disc 60 and the periphery of the disc 60 and thetrajectory back onto the disc 60 is likely to take the material muchcloser to its initial impact position than if a cylindrical wall isused.

The breakdown mechanism described with reference to FIG. 6, whichrelates to generally larger and heavy particles which are deposited frominlet 122 on a central portion of disc 60, can also apply to smallerparticles. The smaller particles will bounce back and forward betweenthe disc in a somewhat similar fashion to that shown in FIG. 6, exceptthe initial impact with the disc is radially outwardly of the centre, soits efficient kinetic energy is imparted to the material to cause thematerial to bounce up towards the wall 40.

When material is ground in the manner in which we described hereinafter,at least some of that ground material moves up the housing 12 to outlettube 16. As previously explained, the outlet tube 16 supplies the groundparticles to the cyclone 14. The cyclone 14 can be used to collect thefine ground particles and also to provide some separation of particlesizes.

FIG. 5 shows another technique for separating particles of differentsizes as the particles travel up the inner surface of wall 40. In thisembodiment, outlets 124 and 126 are formed at different heights abovethe disc 60 in the conical top casing 120. The formation of the outletsin the conical wall 120 is important, because it has been found that ifan outlet is formed in the inverted conical wall 40, or if more than oneoutlet is formed in the inverted conical wall 40, all of the materialtends to exit that outlet and does not separate through the additionaloutlets depending on size. Some of the fine material, as previouslymentioned, may pass the outlet and require extraction by the cyclone orsimply circulate in the grinder. However, if the plurality of outlets,such as the outlets 124 and 126, are formed in the conical wall 120,separation of particle sizes does take place because the relativelylarger particles, as they flow up the inclined wall formed by theconical housing 120, can tend to drop into the outlet 126 with thesmaller particles remaining in the air stream, and then drop into thehigher opening 124 as their energy, or speed of motion in the air streamreduces. The reason why the separation appears to occur in the conicalsection 120 rather than in the section 40 is due to the respectiveangles of the wall and the fact that the inverted cone 40 tends to allowall of the very small particles to exit the first opening the materialcomes across because of the angle that opening makes with respect to thedirection of air travel up the incline wall 40, whereas the angle of thewall 120 allows the even smaller particles to travel past lower openingsin the airflow towards the opening above that lower opening forcollection in the higher opening.

As is shown by FIG. 7, fine particles could be collected by the outlet16 and conveyed to cyclone separator 14 if desired. Whilst the cycloneis suitable for collecting very fine particles, the cyclone could alsobe used for collecting larger particles and the openings 119, 126 or124, previously described, could be connected to the cyclone 16 so thatthe particles collected from that outlet are separated from the airflowin the cyclone 14.

The air and particulate material which exits the outlet 16 is suppliedto the cyclone 14. The air supply through the outlet 16 to the cyclone14 is directed tangentially into the cylindrical cyclone 14 as shown inFIG. 1, so as to create a generally circular or cyclonic flow of air inthe cyclone 14. The circular or cyclonic air flow in the cyclone 14 isalso supported by entry of hot air into the hot air inlet tube 34, whichis also arranged tangentially with respect to the cyclone 14.

As is shown in FIG. 7, the particles which enter the cyclone 14 from thetube 16 are entrained in the air flow which creates the circular orcyclonic air flow within the cyclone 14, or which merges in with thecyclonic air flow caused by the hot air introduced through the inlet 34.

The cyclonic air flow within the housing 14 separates the particles fromthe air flow so that the particles are able to drop under the influenceof gravity into particle outlet 22 whilst the air is able to exit thecyclone 40 through air outlet tube 24.

The outlet tube 24 will generally be at higher pressure than the reducedpressure region in the centre of the housing 12 and the air inlet 18 cantherefore be connected to the outlet tube 24 for the supply of air backinto the housing 12 through the inlet 18. Any very small particles whichare still trapped in the air flow in the outlet 24 therefore have theopportunity to pass back into the housing 12 for reprocessing.

In other embodiments (not shown), as well as or instead of the cyclone14, electrostatic or magnetic precipitators, or gas scrubbers, couldalso be used for removing fine particles. The electrostatic or magneticprecipitators or gas scrubbers could be used in the inlet 18 shown inFIG. 1 to remove the small particles so they do not just continuouslycirculate. Furthermore, such devices may also be used on the outlet 24from the cyclone.

As previously mentioned, if desired, hot air can be supplied to thehousing 12 through hot air inlet 32 (not shown in FIGS. 2 and 3). Thesupply of hot air is useful if it is desired to dry the material whichis being broken down by the grinder and, in particular, if the materialis in a semi-gas or wet condition.

In other applications where the supply of hot air is undesirable (suchas the breakdown of coal or the like, which may ignite or explode duringbreakdown), the valve 30 can be shut off to ensure that no hot air issupplied to the housing 12. In other embodiments, the inlet 32 could beconnected to an inert gas supply for supplying inert gas in the event ofbreakdown of volatile materials such as coal or the like, to eliminatethe possibility of ignition or explosion of the material duringbreakdown in the grinder 12.

FIG. 8 shows a second embodiment which is similar to the embodiment ofFIG. 1. Like reference numerals indicate like parts to those previouslydescribed.

The grinder installation 11 is supported in a support frame 199 whichcould be mounted on wheels or casters 201 to enable the support frameand grinder to be moved from place to place. Alternatively, the supportframe 199 may simply be fixed to the ground or floor. Support frame 199merely supports all of the components of the grinder installation 11. Inthis embodiment, inlet tube 20 is vertical and is connected to a hopper203. The hopper 203 may be connected to the inlet tube 20 by a feedregulating valve 205 so that, if desired, material in the hopper 203 canbe feed in a controlled manner to the housing 12. The outlet tube 16 mayalso have a regulating valve 206 to control flow of ground smallparticles through the outlet 16 to the cyclone 14. A first blower 207 isprovided for blowing air through air tube 208 to the housing 12. The airtube 208 may communicate with at least one of the holes 108 (see FIG. 9in the housing 12). Alternatively, the tube 200 may connect to amanifold (not shown) which in turn communicates with the interior of thehousing 12 to supply air into the housing 12. Air is supplied into theblower 207 through inlet 209 and valve 210. A second blower (not shown)is located behind the blower 207 and air is supplied into the secondblower via inlet 212 and valve 213. The second blower 213 has an outlettube 214 which supplies air into the cyclone 14 for increasing the speedof the vortex or cyclonic airflow within the cyclone 14.

Air exhaust 18 from the housing 12 connects to air exhaust outlet pipe215 from the cyclone 14 and the outlet pipe 215 is connected to a secondcyclone 216. The cyclone 14 has a small particle outlet 217 which isprovided with a gas lock 218 (see FIG. 10), and the cyclone 216 isprovided with a small particles outlet 219 which is also provided with agas lock 218 (see FIG. 11). The gas locks 218 allow the small particlesto pass through the gas locks but not the high pressure air in thecyclones. The cyclone 216 also has an air exhaust 220.

Thus, ground particle which exit the housing 12 through the outlet tube16 are provided to the cyclone 14 where the particles are separated fromthe airflow and which can be collected in a container (not shown)arranged below the particles outlet 217. Air exits the cyclone 14through outlet tube 215 and any very small particles which are stillentrained in that airflow are supplied to the second cyclone 216. Thoseparticles are separated in the cyclone 216 and are collected in acontainer (not shown) below the particles outlet 219. The air suppliedto the cyclone 216 from the outlet tube 215 exhausts from the cyclone216 through exhaust outlet tube 220. The outlet tube 220 may beconnected to a final filter or scrubber for collecting the very fineparticles which may remain entrained in the airflow exhausted from thesecond cyclone 216.

The gas locks 218 are shown in FIGS. 12 and 13 and comprise an inlettube 221 which connects to the outlet 219 (or the outlet 217 as the casemay be), the inlet 221 is in communication with a cylindrical chamber222. The cylindrical chamber 222 has an outlet tube 223. A rotor 224 ismounted for rotation within the cylindrical chamber 222 and has threevanes 224 a, 224 b, and 224 c. The rotor 224 is mounted on an axle 225.As is shown in FIG. 13, the axle 225 is driven by an electrical motor226 so that the rotor 222 rotates about the axis of the axle 225.

Thus, small particle material which enters the inlet 221 collects in thespace 227 between the vanes 224 a and 224 b. The particles which arecollected in the space between the vanes 224 b and 224 c is allowed todrop through the outlet 223 and the space between the vanes 224 a and224 c is empty. Thus, the outlet 223 is always sealed from the inlet 221by the rotor 222 so that relatively high pressure air in the cyclone 216(or 214 as the case may be) is not able to communicate with the outlet223. This allows the fine ground material to simply drop under gravityout of the space between the adjacent pair of rotors as that space comesinto communication with the outlet tube 223 and therefore will not beblown out in a cloud of fine dust, which may otherwise happen if the gaslock 218 was not provided. Thus, the spaces between adjacent vanes 224a, 224 b or 224 c are sequentially filled with fine ground material andare emptied as those spaces move into communication with the outlet tube223 so that the small particles simply drop under the influence ofgravity into the container (not shown) located below the outlet 223.

FIG. 9 is a detailed view of disc 60 within the housing 12. Thisarrangement is basically the same as that shown in FIG. 3 and, onceagain, like reference numerals indicate like parts to those describedwith reference to FIG. 3. However, in this embodiment the inlet 20 isextended by an inlet pipe 20′ which has an outlet adjacent the peripheryof the disc 60. This embodiment is particularly suitable for grindingsmaller particles such as sand or the like which have a size less than10 mm. In this embodiment the material is deposited directly at theperiphery adjacent main grinding zone Z which will actually produce thevery small particles for collection. The grinding zone Z is generallybetween the periphery of the disc 60 and the inner stationary wall 102,and within the confines of the disc 60 (ie. between the top surface andbottom surface of the disc 60). However, the grinding zone Z may extendto a position above the top surface of the disc 60, but still generallybetween the periphery of the disc 60 and the inner stationary wall 102.The sand may be deposited at the periphery because it is already in arelatively small state, as compared to the gross material previouslydescribed which is of much larger size and which needs to be broken downto a smaller size before it is ground in the main grinding zone Z tovery small particles which will eventually be collected at the outlets217, 219 or 220.

The periphery of the disc is spaced from the inner wall 102 by adistance of 10 to 30 mm. However, a larger space could be used dependingon the nature of the material to be ground. The disc is about 400 mm indiameter and is rotated at a speed of about 4500 rpm. The disc has aweight of about 5 to 10 kg. However, obviously larger or smallermachines could be produced by scaling these dimensions.

FIG. 9A shows an underneath view of the disc 60 and, in particular, theconfiguration of the vanes 100. The vanes 100 are configured so theywill drive the air out of the turbine formed by the vanes 100 in thesame direction K as the rotation of the disc. Furthermore, the vanes 100are shaped so that gas particles accelerating, as shown by arrows L,from an inner peripheral portion of the vanes to the periphery of thedisc create sufficient acceleration to enable the air to exit in thedirection of rotation without producing turbulence (as shown by arrowsM). As can be seen in FIG. 9A, the vanes 100 are generally arcuate, withthe radius of curvature generally increasing towards the outer peripheryof the disc so that the exiting air is as near as possible tangential tothe disc 60.

When the disc 60 is rotated, the vanes 100 produce a flow of air fromthe air which enters the holes 108. The blower 207 may be used toprovide an initial speed to the air as the air enters the housing 12 sothat that air is collected by the vanes 100 as the disc 60 rotates toproduce the high speed airflow at the periphery of the disc 60 generallyin the vicinity of the contoured wall 102 which, together with theperiphery of the disc 60, generally defines the main grinding zone Z. Itshould be understood that the blower 217 need not be used and air couldsimply enter the housing 12 through the openings 108 for collection bythe vanes 100. Thus, the vanes 100 and the rotating disc 60 produce agenerally lamina airflow at the periphery of the disc which is very fastimmediately adjacent the periphery of the disc, and most preferably atleast as fast as, if not faster that the speed of the periphery of thedisc. The rotating disc, together with the vanes 100, therefore providesenergy intensification of the air within the housing 12 at the peripheryof the disc in the grinding zone Z. Thus, the stationary air below thedisc 60 and within the housing 12 is therefore accelerated up to highspeed at the periphery of the disc. If the air is introduced with somespeed by the blower 207, then the speed of the air is furtheraccelerated by the disc 60 and vanes 100.

As is shown in FIG. 14, the pressure differential of air below the disc60, where it can be seen that the pressure increases from a relativelylow pressure region 230 inwardly of the disc to a high pressure region232 at the periphery of the disc. The closer or more dense crosshatching in FIG. 14 shows increasing pressure regions extending towardsthe periphery of the disc.

FIG. 15 is a diagram similar to FIG. 14, except that the diagram showsthe speed differential where the speed of the airflow increases from theposition 230 inwardly of the periphery to the region 232 at theperiphery of the disc. Again, the more dense cross hatching showsincreasing speed. The pressure and speed of the airflow at the peripheryof the disc may be in the order of 150,000 Pa and 300 metres per second.

If relatively large particulate material is deposited into the housing12, such as broken glass which may have a size of about 10 mm or largermaterial, initial breakdown occurs due to impact with the disc 60 andthe side wall of the housing 40 as previously described. Small particleswill find their way into the grinding zone Z and further breakdown willoccur due to particle to particle collisions in that zone and alsopossibly some collisions with the wall 102, although these lattercollisions are likely to be much fewer than the particle to particlecollisions. As the particles begin to break down into small particlesizes, the grinding zone Z starts to establish itself.

The manner in which the material is ground in the grinding zone Z willbe described with reference to FIGS. 14 to 17. This form of grinding isapplicable to both the embodiments of FIGS. 1 to 7 and 8 to 13. Smallparticles in the housing 12 will eventually find their way to theperiphery of the disc 60. This can happen by breakdown of large grossmaterial in the manner described with reference to FIG. 6, or bydepositing smaller material through the tube 20′ at the periphery of thedisc 60. In both cases, the material in relatively large particle size,but much smaller than the gross particle size which is broken in themanner described with reference to FIG. 6, therefore tends to enter inthe direction of arrow D either directly from the tube 20′ or afterbeing broken up by impacts with the disc 60, the wall 40 and particle toparticle impact above the disc 60. The kinetic energy of the relativelylarge particles is therefore intensified as the particles near the discperiphery, and the particles are therefore driven by centrifugal forceinto the zone R₁ shown in FIG. 16.

As the particles begin to break down into smaller particle sizes, arange of particle sizes will be created. Some of those particle sizeswill be very small and probably in the order of about 200 to 800nanometres. These particles are entrained in the annular gas flowcreated in the grinding zone Z between periphery 60 a of the disc 60 andthe wall 102. This air flow is made up of molecules of the gases makingup the air and the small particles held in an aerosol suspension withinthe air. If the suspended particles are small enough, this air particlemixture will act generally as a gas within a certain range oftemperatures and pressures, that is, it will obey gas laws relating totemperature and pressure and increase in kinetic energy of all of theparticles when heated. This gas mixture is referred to herein as a heavygas. This heavy gas generally forms in a region R₁ which is radiallyoutwardly of the periphery 60 a of the disc 60. The reason for this isthat the heavy gas is generally pushed out to this region by the gasflow created by the vanes 100. The very small particles which mix withthe air molecules to form the heavy gas generally remain in the regionR₁ outwardly of the periphery of the disc 60 because they are adjacentto a stationary wall, and therefore move more slowly than the newlyentering air from the vanes 100. The heavy gas region R₁ is thereforemoving at a slower speed than the gas in region R₂ and which will form aboundary layer which will become the sheer zone S₂ between the regionsR₁ and R₂ when the larger particles migrated into the grinding zone Zfrom the disc 60. Thus, if heat is added to the heavy gas, kineticenergy is increased, thereby increasing the grinding effect with little,if any, added mechanical energy. The heavy gas therefore generally actslike a normal gas such as air, but is formed by molecular particlescarrying a suspension of larger, but very small particles. The suspendedparticles usually cannot be filtered or settled in devices likecyclones, and are generally analogous to a liquid colloid suspension. Asthe heavy gas region R₁ builds up, the sheer zone S₂ is thereforecreated between the region R₁ and the second region R₂ between the sheerzone S₂ and the periphery 60 a of the disc 60. The region R₁ of theheavy gas particles generally forms radially outwardly of the disc 60 abecause of the relatively small size of those particles. A low frictionair cushion exists in a region R₃ between the wall 102 and the region R₁which moves slower than the heavy gas flow in region R₁ and a sheer zoneS₁ is created between the regions R₃ and R₁. In the region R₃, the airis moving very slowly because of contact with the wall S₁ and thereforethe particles in the region R₁ tend not to move into that region, butremain within the region R₁ between the sheer zone S₁ and the sheer zoneS₂. The larger particles which are initially provided in the region R₂will at random come into contact with the sheer zone S₂ or pass throughthe sheer zone S₂ into the region R₁. At the sheer zone S₂, or if theymove into the region R₁, they are bombarded by the heavy gas and, inparticular, the small particles to cause breakdown of those largerparticles into smaller particle sizes. This will in turn form particlesof varying sizes and again, some of those particles will be of the verysmall size which simply add to the heavy gas in the region R₁ and otherswill be slightly larger particles. The region R₁ therefore fills withparticles, both of a relatively small size to form the heavy gas, andalso slightly larger sizes. Thus, some of the particles which passthrough the sheer zone S₂ or which simply arrive at the sheer zone S₂are comminuted into heavy gas particles by collision with existing heavygas particles in the region R₁ and at the sheer zone S₂. Some of theparticles which are communicated are not sufficiently small to behave asheavy gas particles, and some of those particles will be quickly ejectedback to the region R₂. This is because the differential air speeds ofthe heavy gas and the newly introduced gas from the vanes 100 will havea pressure difference. However, as the number of particles in the regionR₁ and R₂ tends to build up, in the annular flow of air between theperiphery of the disc 60 a and the sheer zone S₁, some of the particleswill tend to spill upwardly out of the sheer zone Z along the wall 102.Movement of the particles in this direction is facilitated by theupwardly directed flow of air which is created by the vanes 100.

The particles which move out of the grinding zone Z will be largelyparticles which have entered the heavy gas region R₁ and which arebroken down into smaller particle sizes, but not sufficiently small toact as a heavy gas, together with some of the heavy gas particles, andalso some of the particles from the region R₂ which are still relativelylarge.

Of those particles which leave the region Z, most of the heavy particleswill tend-to move into a complex field created above the disc 60, andwhich will be described in more detail hereinafter, and will berecirculated back down onto the disc 60 to migrate back to the grindingzone Z for further grinding. However, some of those larger particles,together with small particles, and also some heavy gas particles andsmall particles which are created in the grinding zone Z will eithermove with the upwardly moving air stream to the outlet 16, or beentrained in the exhaust gas exhausted from the housing 12 through theexhaust outlet 18.

Because the disc 60 has a plurality of vanes 100 and is rotatingrelatively fast, a very stable and coherent annular generally laminarflow of air is created at the grinding zone Z which is directed slightlyupwardly relative to the disc 60 and therefore, a stable and coherentannular grinding zone Z is created in the annular region around the disc60 between the periphery 60 a and the wall 102, to therefore form agrinding zone Z which has a substantial size. The continued pumping ofair into the grinding zone from the plurality of vanes 100 ensures thatthe airflow within the grinding zone Z is stable and coherent so thatthe heavy gas region R₁ of heavy gas particles is established andmaintained.

Thus, a stable and coherent grinding zone Z is built up and ismaintained between the periphery of the disc 60 a and the wall 102,which is comprised of the sheer zone S₂ between the larger particles inregion R₂ and the heavy gas within the region R₁. Because the disc 60 isspaced a relatively small distance from the wall 102 and effectivelydefines a uniform annular space between the periphery 60 a and the wall102, and air is continually fed into that space by the vanes 100attached to the rotating disc 60 a uniform and coherent heavy gasannulus is maintained in the region R₁.

Thus, as larger particles move into the region R₂, those particles comeinto contact with the heavy gas in the region R₁ at the sheer zone S₂and are further comminuted by particle to particle contact at the sheerzone S₂ so that those larger particles in the region R₂ contribute morefine particles to the heavy gas in the region R₁. As the region R₁overfills with fine heavy gas particles and small particles which arelarger than the heavy gas particles, those particles begin to spillupwardly along the wall 102.

The high energy environment of the heavy gas annulus in the region R₁will produce other changes in the particles within the region R₁. Someof these changes will involve surface molecular dissociation andsublimation and will result in the production of continuously finerparticles.

The particles remain in the region R₁ for a relatively short timeperiod, and probably significantly less than one revolution of the disc60 (although very small particles may stay in the region R₁for longer),as will be described in more detail with reference to FIG. 18. Theparticles therefore leave the grinding zone Z quite quickly and passthrough the complex vector field above the disc 60. This complex fieldis shown in FIG. 17.

As can be seen from FIG. 17, the particles move out of the region R₁upwardly adjacent the wall 102 to the wall 103 a. The step 103 isprovided to maintain the particles within the region R₁ for a reasonableamount of time to ensure that they do not exit the region R₁ too quicklywhich could prevent the heavy gas in the region R₁ from beingestablished and maintained. However, it should be understood that thecylinder 74 which is provided with the wall portion 102 and the step 103need not necessarily be provided and the housing 12 could simply have aconical or vertical wall which may be provided by the wall 40 of thehousing 12 adjacent the periphery of the disc 60.

As the number of heavy gas particles and small broken down particlesbuild up in the region R₁, the particles generally move upwardly withthe airflow created by the vanes 100 which, as previously described,direct the airflow upwardly relative to the disc 60. The movement of theairflow may also entrain some of the particles from the region R₂. Thefine particles created in the region R₁ with perhaps a few of the largerparticles from the region R₂ will move up the wall 103 a and the wall 40of the housing 12 in bands of rising air 260.

Those particles are entrained in a rotating, generally lamina flow ofstream tubes 280 (which will be described in more detail with referenceto FIG. 18), and exit through outlet tube 16 to be conveyed to the firstcyclone 14. The particles which enter the exhaust outlet tube 18 areconveyed to the second cyclone 216 via the outlet tube 215 from thefirst cyclone 14 as previously described.

The particles which enter the complex vector field above the disc in theregion 250 meet a generally standing wave 270 formed in the air abovethe disc 100. Large particles in those particles which meet the standingwave 270 tend to be moved back to the periphery of the disc 60 and backinto the grinding zone Z for further grinding. The very light fines tendto do a loop as shown by arrow A in FIG. 17, and are extracted throughexhaust tube 18 with the exhaust air from the housing 12.

The larger particle which meets the standing wave 270 and which aredirected back down to the disc 60, moves back to the grinding zone Z aspreviously described, for more grinding until those particles are brokendown into a particle size which will either travel up the wall 40 in themanner previously described, or which will be entrained in the airflowexiting the exhaust outlet 18.

FIG. 18 shows the lamina airflow stream tubes 280 which are created andwhich move up in bands adjacent the wall 40. These stream tubes 280carry the fine particles to the outlet 16. As can be seen in FIG. 18,the stream tubes remain in the grinding zone Z for only a very smalltime period and which may be only 15 to 30° of the rotation of the disc60 (for example, from point C to point D in FIG. 17). These stream tubesare created by the vanes 100 which, as can be seen in FIGS. 3 and 9, areangled upwardly to tend to push the airflow into the grinding zone Z andthen upwardly away from the disc.

FIG. 19 shows an actual measure distribution of small particles andother particles collected from the grinder. FIG. 20 extends this to thefull distribution of small particles and particle sizes. Particles belowa size of about 1.6 microns may not be collected because of their verysmall size and simply pass through all final filtering, and hence do notappear in the experimental actual measured distribution in FIG. 19.However, it is apparent that the distribution is generally in the formof a bell curve distribution, and when extended below the one micronsize, as shown in FIG. 20, obviously much smaller particles than thesmallest size actually measured are present. As can be seen from FIG.20, the heavy gas in the region R₁ is made up from the heavy gascomponents shown in FIG. 20 and labelled G which are minute particles orfines having a size of less than about 800 nanometres. The heavy gasparticles which travel up the wall 102 to the outlet 16 probably willnot be collected because of their very small size and will simply passthrough the filtering stations and exit with the exhaust air. However,these could be collected by electrostatic or magnetic devices or waterentrapment.

In the preferred embodiments, the vanes 100 are directly upwardly aspreviously described. However, the vanes could be arranged substantiallyhorizontally, and the angle of the wall 102 inclined more than thatshown in the drawings so as to send the gas stream produced by the vanes100 upwardly into the grinding zone Z.

If desired, pins or other like elements may extend upwardly from thebase of the housing into the grinding zone Z at about the vicinity ofthe sheer zone S₂ to create some turbulence at the sheer zone whichtends to assist the mixing of particles from the region R₁ at the sheerzone with the heavy gas in the region R₂ to comminute the heavyparticles into smaller particles at the sheer zone S₂ in the region R₁.

The preferred embodiment of the apparatus may also be used in a vacuum.If the apparatus is used in a vacuum, the initial grinding processdescribed with reference to FIG. 6 will still occur. However, to obtainthe additional grinding in the grinding zone Z, it will be necessary toestablish the heavy gas in the region R₁ by the introduction ofparticles which could form a functional heavy gas in the region R₁. Thismay be achieved by directing suitable fine particles through the inlet108 and then through the vanes 100 to the periphery of the disc so thatthe particles establish the heavy gas and continue to act as thetransport system in the manner described above. This embodiment wouldonly be used in environments where it would not be desirable to have anyother gas involved in the process. The heavy gas may be formed by aninert gas (for example, argon) and added particles of heavier material,or alternatively, if no gas at all is desired and a true vacuumrequired, the heavy gas could be formed by minute particles of asuitable material such as silicates or iron or the like.

If it is desired to grind very light particles such as feathers or wheatflour, and very fine particles required, it is necessary to establishthe heavy gas other than from the material which is to be ground in thesame manner as described above. In such embodiments, the heavy gas maybe formed by adding water or some other particle such as the silicatesor the like.

As is shown in FIG. 21, the particle size collected by the cyclone 14and which appear at the outlet 217 are generally in the range of 0 to 30microns (with those over 30 microns being ignored because they arerare), with the majority of the particles being in the range of 5 to 20microns. As shown in FIG. 22, the particle size of the particlescollected at the particles outlet 219 of the second cyclone aregenerally in the range of 0 to 10 microns, with a majority being lessthan 5 microns in size.

Since modifications within the spirit and scope of the invention mayreadily be effected by persons skilled within the art, it is to beunderstood that this invention is not limited to the particularembodiment described by way of example hereinabove.

1. An impact particle grinder, including; a housing having an innerwall; a grinding disc mounted in the housing for rotation within thehousing; means for rotating the grinding disc; an inlet for depositingmaterial onto a first location on the rotating disc, so kinetic energyis supplied to the material from the disc to fling the material againstthe inner wall of the housing, and material deflected from the housingfalls back onto the disc at a second location radially outwardly of thefirst location so that further kinetic energy is imparted to thatmaterial to provide an energy intensifying process as material continuesto impact against the inner wall of the housing and fall back on aradially more outward part of the rotating disc, and wherein particle toparticle collisions within the housing and collisions with the rotatingdisc and inner wall break down the material to produce small particles;and outlet means for discharge of the small particles from the grinder.2. The grinder of claim 1 wherein the inner wall of the housing is ofinverted conical shape so that deflection of material from the innerwall tends to direct the material to the second location which is asmall distance from the first location, thereby producing a significantnumber of impacts of the material with the disc as the material bouncesbetween the disc and the inner wall.
 3. The grinder of claim 1 whereinthe grinder includes hot air inlet means for introducing hot air intothe housing adjacent the disc for drying the material as the material isground.
 4. The grinder of claim 1 wherein the grinder also includesinert gas introduction means for introducing inert gas to mix with theground particles.
 5. The grinder of claim 1 wherein the outlet means isarranged above the disc.
 6. The grinder of claim 1 wherein the outletmeans comprises a plurality of outlets which are arranged at differentheights above the disc so that particles of different sizes arecollected in each of the outlets, the outlets being provided in ahousing wall portion which is of conical shape.
 7. The grinder of claim1 wherein the outlet means may include a recirculator for recirculatingsmall particles from the outlet means back to the housing forreprocessing in the housing.
 8. The grinder of claim 1 wherein theoutlet means is connected to a cyclone particle collector.
 9. Thegrinder of claim 8 wherein the cyclone particle collector comprisesmeans for creating a circular flow of air in the cyclone, inlet meansconnected to the outlet means for receiving particles from the housingand for conveying the particles into the cyclone for circulation in thecircular air flow in the cyclone, an air outlet tube in the cyclone anda particle outlet in the cyclone, and wherein particles trapped in thecircular flow of air are conveyed about the cyclone with the circularflow of air and separated from air flow so that the particles can becollected in the particle outlet and air exit the cyclone through theair outlet.
 10. The grinder of claim 9 wherein the air inlet means forcreating the circular flow of air comprises a hot air inlet and a heaterfor heating air for supply to the hot air inlet.
 11. The grinder ofclaim 1 wherein the disc has an outer periphery which is in closeproximity to the inner wall of the housing so that when the disc isrotated by the rotating means, an annular rotating stream of air isformed between the periphery of the disc and the inner wall, so a heavygas region is created between the periphery of the disc and the innerwall so that when particles enter the space between the disc and theinner wall, they contact the heavy gas in the region to furthercomminute the particles to smaller particle sizes.
 12. The grinder ofclaim 11 wherein an air inlet means is provided below the disc in thehousing for allowing air to enter the housing from below the disc tocause the air annulus to spill up the inner wall of the housing so thatground particles trapped in the rotating stream of air are carried bythe spill of air to the outlet means.
 13. The grinder of claim 1 whereinthe disc includes a plurality of vanes for imparting momentum to the airwhen the disc rotates to create the annular rotating stream of airbetween the periphery of the disc and the wall, said vanes having anarcuate shape for directing air in the same direction as intendedrotation of the disc for accelerating gas particles from an innerperipheral portion of the vanes to the periphery of the disc to createsufficient acceleration to enable the gas to exit the vanes in thedirection of rotation of the disc without producing any substantialturbulence.
 14. The grinder of claim 13 wherein the vanes are angledupwardly relative to the horizontal so that the rotating stream of airis directed upwardly above the disc to facilitate the spill of air upthe inner wall.
 15. The grinder of claim 1 wherein the inner wall of thehousing includes a separate cylindrical wall which includes a contouredwall portion for trapping material so the material remains in theannular airflow for a long period to break down the material to smallerparticle sizes, before the smaller particles travel in the spill of airup the inner wall to the outlet.
 16. A method of impact grinding amaterial, comprising; supplying the material to a grinder which has ahousing having an inner wall and a rotating disc mounted in the housing;wherein the material supplied is deposited onto a first location on therotating disc, so kinetic energy is supplied to the material from thedisc to fling the material against the inner wall of the housing, andmaterial deflected from the housing falls back onto the disc at a secondlocation radially outwardly of the first location so that furtherkinetic energy is imparted to that material to provide an energyintensifying process as material continues to impact against the innerwall of the housing and fall back on a radially more outward part of therotating disc, and wherein particle to particle collisions within thehousing and collisions with the rotating disc and inner wall break downthe material to produce small particles; and collecting the smallparticles from the grinder.
 17. A grinder for producing small particlesfrom material, comprising: a housing having a substantially inner wall;a disc mounted in the housing and having a periphery adjacent the innerwall; a motor for driving the disc so the disc rotates about asubstantially vertical axis; a plurality of vanes on the disc forcreating an annular flow of gas between the periphery of the disc andthe inner wall to create a grinding zone between the inner wall and theperiphery of the disc; an inlet in the housing for receiving theparticulate material, so the particulate material is able to migrate tothe grinding zone between the periphery of the disc and the inner walland be broken down to small particles; and a small particles outlet forallowing outlet of the small particles from the housing.
 18. The grinderof claim 17 wherein the inlet comprises an inlet tube extending withinthe housing from an upper portion of the housing to a position adjacentthe periphery of the disc.
 19. The grinder of claim 17 wherein thehousing has a gas inlet below the disc and the vanes are located on alower surface of the disc for collecting the gas and directing the gasto the periphery of the disc to provide energy intensification to thegas so that the gas at the periphery of the disc moves with high speed,and the gas adjacent the stationary inner wall is at relatively lowspeed, said vanes having an arcuate shape for directing air in the samedirection as intended rotation of the disc for accelerating gasparticles from an inner peripheral portion of the vanes to the peripheryof the disc to create sufficient acceleration to enable the gas to exitthe vanes in the direction of rotation of the disc without producing anysubstantial turbulence.
 20. The grinder of claim 17 wherein the grindingzone comprises a first region between the wall of the housing and anintermediate location between the wall and the periphery of the disc forestablishing a heavy gas, and a second region between the periphery ofthe disc and the intermediate location for receiving particles from thedisc so those particles can move into the heavy gas and be ground intosmall particles.
 21. The grinder of claim 20 wherein a sheer zone iscreated at the intermediate location between the first and secondregions.
 22. The grinder of claim 17 wherein the vanes are located onthe lower surface of the disc and are directed upwardly so that thevanes direct the gas to the periphery of the disc and upwardly relativeto the disc so that the annular flow of gas created by each of the vanesbetween the disc and the inner wall, and within the confines of the discfor a short time period and then moves upwardly relative to the disc inannular fashion adjacent the inner wall of the housing.
 23. The grinderof claim 17 wherein the housing has an exhaust gas outlet arrangedsubstantially centrally of the disc.
 24. The grinder of claim 18 whereina standing wave is created between the exhaust gas outlet and theperiphery of the disc so that particles which are broken down intosmaller particles in the grinding zone are able to move upwardly withthe airflow adjacent the inner wall of the housing to the outlet, ormove inwardly of the disc where they meet the standing wave and aredirected down back to the upper surface of the disc and move along theupper surface of the disc back to the grinding zone for furthergrinding, or travel with the exhaust gas to the exhaust outlet.
 25. Thegrinder of claim 17 wherein the outlet is connected to a first cyclonefor separating gas from the small particles so the small particles canbe collected at an outlet of the first cyclone.
 26. The grinder of claim23 wherein the exhaust gas outlet is connected to a second cyclone sothe gas and small particles can be separated in the second cyclone toenable the small particles to be collected at an outlet of the secondcyclone.
 27. The grinder of claim 25 wherein the first cyclone has a gasexhaust outlet which is connected to the second cyclone so that anysmall particles which remain in the gas exhausted from the first cycloneare fed to the second cyclone for separation from the gas in the secondcyclone.
 28. The grinder of claim 27 wherein the outlet from the firstcyclone includes a gas lock for preventing high pressure gas fromexiting the outlet and blowing small particles into the atmosphere. 29.The grinder of claim 27 wherein the outlet from the second cyclone alsoincludes a gas lock for preventing high pressure gas from exiting thesecond cyclone through the outlet.
 30. A method of producing smallparticles from material, comprising: supplying the material to a housinghaving a substantially inner wall and a rotating disc mounted in thehousing and having a periphery adjacent the inner wall so that the disccreates an annular flow of gas between the periphery of the disc and theinner wall to create a grinding zone between the inner wall and theperiphery of the disc; allowing the material to migrate to the grindingzone between the periphery of the disc and the inner wall and be brokendown to small particles; and collecting the small particles from thehousing.
 31. The method of claim 30 wherein the method includes allowingthe gas to enter the housing from below the disc and providing vanes ona lower surface of the disc for collecting the gas and directing the gasto the periphery of the disc to provide energy intensification to thegas so that the gas at the periphery of the disc moves with high speed,and the gas adjacent the stationary inner wall is at relatively lowspeed, and wherein the grinding zone is created by the establishment of:(a) a heavy gas formed from a mixture of the gas and minute particles ina first region between the inner wall and an intermediate positionbetween the disc and the inner wall; (b) a second region for receivinglarger particles to be ground into the smaller particles, between theintermediate position and the periphery of the disc; (c) a sheer zonebetween the first and second regions; and wherein particles in the firstregion pass through the sheer zone, and some are comminuted into heavygas particles and others which are not sufficiently small to behave asgas particles are either ejected back to the first region for furthergrinding as those particles re-enter the heavy gas through the sheerzone, or move out of the grinding zone for collection from the housing.32. The method of claim 31 wherein the annular flow of gas created byeach of the vanes between the disc and the inner wall is maintainedwithin the confines of the disc and at the grinding zone for a shorttime period and then moves upwardly relative to the disc in annularfashion adjacent the inner wall of the housing for collection from thehousing.
 33. The method of claim 31 wherein the method also comprisesextracting gas from an exhaust outlet arranged substantially centrallyof the disc.
 34. The method of claim 33 wherein the method furthercomprises creating a standing wave in the gas above the disc between theexhaust outlet and the periphery of the disc so that particles which arebroken down into smaller particles in the grinding zone move upwardlywith the airflow adjacent the inner wall of the housing for collectionfrom the housing, or move inwardly of the disc where they meet thestanding wave and are directed down back to the upper surface of thedisc and then move along the upper surface of the disc back to thegrinding zone for further grinding, or travel with the exhaust gas tothe exhaust outlet.
 35. The method of claim 30 wherein the methodfurther comprises supplying the collected small particles to a firstcyclone for separating gas from the particles so the particles can becollected at an outlet of the first cyclone.
 36. The method of claim 33wherein small particles collected at the exhaust outlet are supplied toa second cyclone so the gas and small particles can be separated in thesecond cyclone to enable the small particles to be collected at anoutlet of the second cyclone.
 37. A grinder for producing smallparticles from material, comprising: a housing having an inner wall; arotatable mechanical member in the housing having a periphery adjacentthe inner wall; a drive for driving the rotatable member for causing therotatable member to create an annular flow of air between the peripheryof the member and the inner wall, and for establishing a grinding zonebetween the inner periphery and the wall which comprises: (a) a firstregion in which a heavy gas is established, the first region beingbetween the inner wall and an intermediate position between theperiphery of the member and the inner wall; (b) a second region forreceiving relatively large particles compared to the particles whichmake up the heavy gas, the second region being between the intermediateposition and the periphery of the mechanical member; and (c) a sheerzone between the first and second regions at the intermediate location;and wherein the relatively large particles received in the first regioncome into contact with the heavy gas particles across the sheer zonewhere the relatively heavy particles are comminuted into smallerparticles, some of which add to the heavy gas within the first regionand the other of which form small particles of a size which do notbehave as a heavy gas, and wherein the small particles, together withsome of the particles which make up the heavy gas and other largerparticles from the first region move out of the grinding zone with anannular flow of air from the grinding zone and travel to a firstcollection outlet for collection or fall back to the mechanical memberand again travel to the first region for further grinding in thegrinding zone.
 38. The grinder of claim 37 wherein the rotatable membercomprises a disc having vanes for creating the annular flow of airbetween the periphery of the disc and the inner wall, said vanes havingan arcuate shape for directing air in the same direction as intendedrotation of the disc for accelerating gas particles from an innerperipheral portion of the vanes to the periphery of the disc to createsufficient acceleration to enable the gas to exit the vanes in thedirection of rotation of the disc without producing any substantialturbulence.
 39. The grinder of claim 38 wherein the housing has anexhaust gas outlet for exhausting air from the housing in which somefines are entrained.
 40. The grinder of claim 38 having a separatorconnected to the first outlet for separating small particles and aircollected from the first outlet.
 41. The grinder according to claim 39wherein the exhaust outlet is connected to a second separator forseparating small particles collected at the exhaust outlet from exhaustair exhausted through the exhaust outlet.
 42. A method of grindingmaterial, comprising: creating a grinding zone having a first annularregion in which an annular flow of heavy gas is established and a secondregion spaced from the first region by a shear zone; directing thematerial into the grinding zone so the material passes from the secondregion to the first region across the shear zone into the annular flowof heavy gas and is comminuted into smaller particles by contact betweenheavy gas particles in the heavy gas and the material; and collectingthe comminuted particles.
 43. The method according to claim 42 whereinthe grinding zone comprises a second annular region arranged radiallyinwardly with respect to the first region in which the material canlocate for movement into the heavy gas in the first region forcomminution whilst in the heavy gas so that the comminution createsfurther heavy gas particles to maintain the annular flow of heavy gaswithin the first region, as well as the small particles which move outof the grinding region for collection.
 44. The method according to claim43 wherein some of the small particles which move out of the firstregion, together with some particles of material from the first regioncirculate within the housing and move back into the grinding zone forfurther grinding before those ground particles are collected from thehousing.
 45. The method according to claim 42 wherein the heavy gas isestablished by the initial supply of material to the housing and thebreakdown of that material within the housing to minute particles whichform the heavy gas in the first region.
 46. The method according toclaim 42 wherein the heavy gas is established by supply of minuteparticles separate to the material to be ground.
 47. The methodaccording to claim 44 wherein the grinding zone is established by arotatable disc arranged within the housing which has a periphery spacedfrom an inner wall of the housing and wherein the grinding zone isformed from the first region containing the heavy gas at a locationbetween the wall of the housing and an intermediate location between thewall and the periphery of the disc, the second region is establishedbetween the intermediate position and the periphery of the disc, and thesheer zone is established at the intermediate position between the firstand second regions.
 48. The method according to claim 47 wherein thegrinding zone includes a third region between the inner wall of the discand the first region, and a sheer zone at the boundary between the firstregion and the third region.
 49. A grinder for producing small particlescomprising: a first region for establishing a heavy gas, a second regionspaced from the first region and a shear zone between the first andsecond regions when the grinder is in use; a material inlet for deliverymaterial so the material passes to the first region for grinding; and anoutlet for collecting the small particles.
 50. The grinder of claim 49wherein the region is an annular region, and an air flow producer isprovided for producing an annular flow of air in the region for.establishing and maintaining a coherent and stable annular heavy gasregion.
 51. A grinding installation for producing small particles frommaterial, comprising a grinder having: (a) a housing having a stationaryinner wall; (b) a disc mounted in the housing and having a peripheryadjacent the inner wall; (c) a motor for driving the disc so the discrotates about a substantially vertical axis, and whereby small particlesare produced by breakdown of material impacting with the disc and theinner wall and/or in a grinding zone between the periphery of the discand the inner wall; (d) an air inlet in the housing; (e) an air exhaustoutlet from the housing; and (f) a particle outlet from the housing; afirst separator connected to the particle outlet for separating air fromthe small particles and for delivering the small particles to a smallparticles outlet; and a second separator connected to the exhaust airoutlet for separating small particles in the exhaust air from theexhaust air and delivering the small particles to a second smallparticles outlet.
 52. The installation of claim 51 wherein the firstseparator has a first exhaust air outlet and the first exhaust airoutlet is connected to the second separator.
 53. The installation ofclaim 51 wherein the first separator comprises a cyclone separator. 54.The installation of claim 51 wherein the second separator comprises asecond cyclone separator.